Visibility meter



July 22,- 1941. s. MlLLR VISQBILITY METER 2 sheets-snaai 1 Filed Dec.1'7. .1,940

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' y VISIBILITY METER Filed Dec. 17, 1940 2 Sheets-Sheet? agg `12fn I/////////////AIT 4. 2- l i giga INVENT'OR STANLEY- MILLER ATTORN EYSPatentedk July 22, 1941` UNITED' STATES PATENT p OFFICE VISIBILITY METERstanley Miner, Missoun. Mm. Application December 17, 1940, Serial No.370,527

(ci tia-zal (Granted under the act of March 3, 1883, as amended April30, 1928; 37u 0. G. 757) 4 Claims.

This application is made under .the act of March 3, 1883, as amended bythe act of April Without the payment to me of any royalty.

thereon.

This invention is of a device for determining the amount of haze betweentwo given points and the visibility distance of objects, and which can,incidentally, be used as a range finder.

'I'he general object of this invention is the provision of a deviceuseful for the purposes mentioned, which is simple in construction andoperation, easy to manufacture, and which does not depend upon personalaptitude for obtaining proper and uniform results.

This invention is based on the principle that under a given set ofconditions the .ease with which an object of specified size can be seenwith the naked eye is determined by the amount of haze that existsbetween the eye and the object and the distance of the object from theeye.

In the accompanying drawings there is illustrated an embodiment of thisinvention, in Which:

Figure 1 is a front elevation view,

Figure 2 is a sectionalong the line Figure 1.

Figure 3 is a ure 1,

Figures 4 and 5 are longitudinal sections of alternate types of theoptical wedge, comprising one of the elements of the invention, and

Figure 6 is a fragmentary view illustrating a modification of` theextensible scale member forming one of the elements' of this invention.

Referring with more particularity to the drawings in which like numeralsdesignate like parts, the numeral Il! designates a vertical column orsection along the line 3--3 of Figbase to which is secured an opticalwedge Il.`

The wedge ll is supported in an upright position against the column iand its density varies uniformly from the top to the bottom, the topl ofthe wedge being the area of greatest clearness and the bottom of thewedge the area, of greatest density. The optical wedge may be of anydesired type. The type illustrated in Figures 1, 2, and 3 is a taperedpiece of glass I2 having a. uniform haze coloring so that light passingtherehaving a haze gradient from one end to the other. The typeillustrated in Figure 5 comprises a. triangular vessel I4 which isillled with a haze-colored liquid i5.

In back of the wedge Il there is disposed an eyepiece, which in theaccompanying drawings is shown to consist simply of a plate I6 having ahorizontal slit il therethrough. This plate i6 carries a pointer i8 andis comounted with a rider i8, slidably operating on the column l0 in avertical direction, substantially as shown. In line with the slit il andthe optical wedge Il e there is disposed in ront ofv said Wedge apicthrough at a given point is obstructed in anamount corresponding to.the thickness of the glass at that point. The type illustrated inFigure 4 is a piece of glass i3 of uniform thickness ture mounting 20,which is secured to the rider I9 so as to move therewith. Thereis alsomounted on the rider 19,. at the front of the instrument, anothereyepiece for viewing distant ob jects, similar to the eyepiece abovementioned, consisting of a plate 2l with a horizontal slit 22. The slitsi'l to 22 are so positioned relative to each other that they willaccommodate the two eyes of the operator. There is fixed with respect tothe wedge il a vertical scale 23 graduated from the'bottom to the top inunits of visibility distance corresponding to the optical densitygradient of the wedge il. Adjacent to this scale 23 there is mounted atthe top of the instrument an extensible scale 24, which may be 'ofrubber or other suitable material. This scale is affixed at its top tothe frame 25 of the device and is free at the bottom where it isprovided with a handle 2S. By grasping the handle 26 and exerting adownward force, the member 24 may be elongated to any desired length.This scale 24 is graduated from the top to the bottom in units ofdistance. When the length of the scale 24 is changed, the spacing of thegraduations change correspondingly, thus providing the necessaryvariability for the operation of the device.

In operation, the mounting 20 is provided with a photograph or picture21 which has substantially the same color and texture of the view wherevisibility is to be determined, that is-to say, of the object Whosevisibility is to be determined from a. given point. For this purpose itis not necessary for the picture or photograph to be of the exact objectso long as the color and textureare substantially the same. To use thedevice, the observer looks through the slit l1 with one eye and throughthe slit 22 with the other, the slit 22 being directed at an object ofknown vdistance from the observer. The rider I9 is then moved verticallywith respect to the wedge il until the clearness of the view seenthrough the slit i1 is substantially the same as the clearness of theview through the slit 22. The position of the rider I9 atthis point is afunction of the amount ot haze existing between the eye and the object.By extending the scale 2l until the distance of the object viewedthrough the slit 22, represented on the scale 24, is opposite the markeri8, lthe position oi every point onthe scale 24 will be a function oithe amount or haze between the observer and objects whose distance fromthe observer is represented by these points, assuming that the haze isuniform.

To determine visibility distance, that is, the maximum distance at whichan object can be seen, it is necessary to use the scale 2l. Aspreviously indicated, this scale is graduated in units of visibilitydistance. Every point' on the scale 23 indicates the distance at whichan object can 1. A device of the character described, comprising anoptical wedge, a picture mounting on one side and an eyepiece on theother side of said wedge for observing a picture on said mountingthrough said wedge, said eyepiece and mounting being commovable on saidwedge, another eyepiece commovable with the iirst mentioned eyepiece forviewing a distant object, said picoi distance.

just be seen when the amount oi haze exist-` ing between the eye ci theobserver and the object is equal to the density of the optical wedge liat that point. This scale may be graduated empirically for theparticular type of objectsV upon which determinations are to be made.For example, in forestry, this scale may be graduated for smoke for usein forest ilre work and can be interchanged with scales graduated tordiilerent objects.

By adjusting rideri! to the point where the haze of the optical wedgeequals the haze between the observer and an object of known distance andextending the scale 24 so that this distance as represented on the scale24 is opposite the marker i8, the visibility distance is determined atthe point where the same number on the scales 23 and are opposite eachother.

Objects at distances below this point on the scale 24 would be indicatedas being invisible because of the existence of too much haze.

In using this instrument, it may be desirable to proportion the scale 24diiIerently iordlierent conditions. This may be done by increasing thewidth of the scale 24, subdividing it in vertical rows and proportioningeach row as desired. To avoid confusion in using such a scale, adiierent arrangement may be employed, as illustrated in Figure 6. Inthis modiiication, the member 2l, corresponding to the extensible scale24 in Figures 1, 2, and 3, is made with a square or rec-- tangular crosssection to provide iour scales, 2|, In, 3|, and 32, one on each face.Other shapes may be used, such as pentagonal, hexagonal, and so forth,if additional scales are desired. The top of the member 2l is securedto` a stub shaft 33, which is rotatably mounted on topp! the frame I4.In this manner, any face of the member 28 may be turned in alignmentwith the scale 23. Any other type of connection may be made between themember 2l and the frame Il, such as ball and socket, swivel, andvsoiforth, thetype illustrated being merely Bugestive'.

I! desired, this'device can also be used as a range ander. This is doneby nrstdetermming 24 opposite the pointer ,il is the range or distanceof the object from'the observer.

f 2. A device of the character described, com- A prising an opticalwedge, a picture mounted on one side and an eyepiece on the other sideoi said wedge for viewing said picture through said wedge, said picturerepresenting a clear view oi an object free from intervening haze andhaving a color and texture substantially the same as the view Wherevisibility is to be determined, said eyepiece and picture beingcommovable on said wedge, another eyepiece ior viewing a distant object,said other eyepiece being commovable with the eyepiece adjacent thewedge, a scale adjaf cent said wedge having designations correspondingto the gradient of optical density oi said wedge, and an extensiblescale adjacent the iirst scale, said extensible scale being graduated inunits of distance.'

3.' A device oi the character described, comprising an optical wedge, apicture mounting on one side and an eyepiece on the other side oi saidwedge for observing a Ipicture xon said mounting through said wedge.said eyepiece and mounting being commovable on said wedge, anothereyepiece tor viewing a distant object, said other eyepiece beingcommovable with the eyepiece adjacent the wedge, said picture.representing a clear view of an object (ree from intervening haze andhaving acolor and texture sublstantially the same as the view wherevisibility is to be determined, a'scale adjacent said wedge havingdesignations corresponding'to the gradient of optical density oi saidwedge, an extensible member adjacent said scale, said extensible,

ing through said wedge, said eyepiece and molmting being commovable onsaid wedge, another eyepiece tor viewing a distant object, said othereyepiece being commovable with the eyepiece adjacent the wedge, saidpicture representing a clear view oi an object iree from interveninghase and having a color and texture substantially the same as the viewwhere visibility is to be determined, a scale adjacent said wedge havingdesignations corresponding to the gradient Having thus described myinvention, I cilaim:

oi' optical density of said wedge, an extensible s'rsmr

